The copper-free Sonogashira cross-coupling reaction promoted by palladium complexes of nitrogen-containing chelating ligands in neat water at room temperature

Article abstract of DOI:10.1039/c3dt52970c

The commercially available 2,2′-dipyridylamine was used as a supporting ligand in the palladium-catalyzed Sonogashira cross-coupling reaction. The reactions between aryl iodides and terminal alkynes with different steric hindrance can be efficiently performed in the absence of copper in neat water at room temperature. The superior catalytic performance of the catalytic system was attributed to water solubility of the palladium 2,2′- dipyridylamine complex. Palladium nanoparticles with small size and narrow size distribution were formed after the cross-coupling reaction.

Full text of DOI:10.1039/c3dt52970c

Dalton
Transactions
View Article Online
View Journal
PAPER
The copper-free Sonogashira cross-coupling
reaction promoted by palladium complexes of
nitrogen-containing chelating ligands in neat
water at room temperature†
Cite this: DOI: 10.1039/c3dt52970c
Hong Zhong, Jinyun Wang, Liuyi Li and Ruihu Wang*
The commercially available 2,2’-dipyridylamine was used as a supporting ligand in the palladium-cata-
lyzed Sonogashira cross-coupling reaction. The reactions between aryl iodides and terminal alkynes with
different steric hindrance can be efficiently performed in the absence of copper in neat water at room
temperature. The superior catalytic performance of the catalytic system was attributed to water solubility
of the palladium 2,2’-dipyridylamine complex. Palladium nanoparticles with small size and narrow size
distribution were formed after the cross-coupling reaction.
Received 22nd October 2013,
Accepted 7th November 2013
DOI: 10.1039/c3dt52970c
www.rsc.org/dalton
Organic reactions in water are of highly practical value
since most wastes per mass unit product in the chemical
Introduction
Transition-metal-catalyzed cross-coupling reactions have been industry result from organic solvents.8 Although the reaction
considered as one of the most valuable and straightforward rates in water may be slower than those in organic solvents or
methods for the formation of carbon–carbon or carbon–nitro- biphasic aqueous systems, water is regarded as the most envir-
gen bonds in modern organic synthesis.1,2 Among them, onmentally benign and cheap medium. Organic reactions in
the palladium-catalyzed Sonogashira cross-coupling reaction neat water usually place significant demands on the solubility
between aryl halides and terminal alkynes is an efficient and of substrates and catalysts, and the use of water-soluble coordi-
convenient approach for the introduction of the acetylenic nation complexes is a common route to the development of
moiety into many biologically important compounds and the catalytic systems in water.9 Much effort has been devoted to
engineered materials.2–4 Traditionally, smooth accomplish- the design and synthesis of water-soluble ionic compounds
ment of the reaction has required the presence of both palla- containing sulfonate, carboxylate and ammonium to serve as
dium and copper, which resulted in contamination of the the supporting ligands of palladium in the cross-coupling reac-
coupling products with metal residues as well as a side reac- tions in neat water.10–12 Very recently, we have prepared a
tion of Glaser-type oxidative dimerization of the alkyne sub- series of water-soluble palladium nitrogen-containing chelat-
strates. These undesirable by-products are difficult to separate ing complexes,12 which showed high catalytic activity and
from the target products due to their similar chromatographic chemical selectivity in catalysis in neat water in comparison
mobility.4 Considerable effort has been devoted to developing with their hydrophobic analogues. In addition, the catalytic
a copper-free Sonogashira cross-coupling reaction under mild activity and selectivity can be modified and tuned by varying
conditions, especially for the expensive or commercially the steric and electronic properties of the nitrogen-containing
unavailable terminal alkynes. However, most of the reactions ligands as well as their coordination ability with metal ions,
were performed in organic solvents or mixed organic/aqueous which greatly enhances the scope of catalysts for different cata-
solvents,5 and neat water is seldom used as a reaction medium lytic applications, but they are not encouraging for the Sonoga-
in the Sonogashira cross-coupling reaction.6,7
shira cross-coupling reaction in neat water. In our continuous
study to explore the environmentally friendly catalytic
systems,12,13 we found that the palladium 2,2′-dipyridylamine
complex is soluble in neat water under ambient conditions,
though 2,2′-dipyridylamine and palladium sources are insolu-
ble (Scheme 1). This provides a possibility for development of
the catalytic systems in water. Dpa was well known for its
remarkable binding ability to transition metal ions. Although
dpa has been covalently attached to various inorganic or
State Key Laboratory of Structural Chemistry, Key Laboratory of Coal to Ethylene
Glycol and Its Related Technology, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Science, Fuzhou, Fujian 350002, China.
E-mail: ruihu@fjirsm.ac.cn; Fax: (+) 86-591-83714946
†Electronic supplementary information (ESI) available: NMR data of the cross-
coupling products and details of theoretical calculations. See DOI: 10.1039/
c3dt52970c
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Scheme 1 The images for (a) Pd(NH3)2Cl2 in H2O; (b) Pd(NH3)2Cl2 was
oscillated in H2O for 24 h; (c) Pd(NH3)2Cl2 and dpa were oscillated in
H2O for 24 h.
organic supports to serve as the coordination group of palla-
dium(II) or palladium NPs,14 dpa is seldom chosen as a single
supporting ligand in catalysis despite the crystal structure of
its palladium(II) coordination complex being reported.15
Herein, we use the soluble Pd(NH3)2Cl2–dpa complex as a pre-
catalyst for the Sonogashira cross-coupling reaction in the
absence of both copper and organic solvents at room
temperature.
Fig. 2 HOMO and LUMO for dpa and Pd–dpa (isovalue = 0.02).
Table 1 Screening of reaction conditions in the Sonogashira cross-
coupling reactiona
[Pd] amount
(mol%)
Entry
Pd source
Base
Yieldb (%)
Results and discussion
1
2
3
4
5
6
7
8
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
PdCl2
Pd(cod)Cl2
Pd(OAc)2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
Pd(NH3)2Cl2
1
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
(i-Pr)2NH
(n-Bu)3N
NaOAc
KOH
K3PO4
Cs2CO3
Bu4NOH
NEt3
100
95
51
87
76
81
26
30
<1
<1
5
In order to obtain a better understanding of the electronic
characteristics of dpa and its palladium(II) complex (Pd–dpa),
the charge distributions and molecular orbital analyses of
dpa and Pd–dpa based on the optimized structures were
implemented using Gaussian 03.16 As shown in Fig. 1 and
Table S1 in ESI,† the nitrogen atoms in both dpa and Pd–dpa
possess a negative charge, in which the pyridyl nitrogen atoms
in Pd–dpa are more negative (−0.50062 and −0.50064e) than
those in dpa (−0.46162 and −0.46163e) owing to the coordi-
nation of palladium(II). However, the amine nitrogen atom
in Pd–dpa (−0.61948e) is less negative than that in dpa
(−0.64026e). Two Cl− ions possess the same negative charge
(−0.52523e) in Pd–dpa, and the positive charge of palladium(II)
is 0.70234e, which is close to those in similar palladium
chelating complexes.12 The highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO)
0.1
0.01
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
9
10
11
12
13
14c
7
<1
72
a Reaction conditions: iodobenzene (0.50 mmol), phenylacetylene
(0.75 mmol), base (1.50 mmol), and H2O (2.0 mL) at 25 °C for 6 h
under N2; the molar ratio of [Pd]/dpa is 1 : 1. b GC yield. c No water was
added.
have shown that HOMO and LUMO in dpa are shared owing to the reaction was performed using 1 mol% Pd(NH3)2Cl2 and
the conjugative effect. However, HOMO in Pd–dpa consists dpa in the presence of NEt3 in neat water at 25 °C for 6 h, 1,2-
primarily of the contribution from the PdCl2 group, and a diphenylethyne was obtained in a quantitative yield (entry 1),
delocalization over PdCl2 and dpa was observed in the LUMO and no side products of diynes or enynes were detected.
of Pd–dpa (Fig. 2).
Decreasing the loading of palladium and dpa to 0.1 and
Catalytic performances of Pd–dpa were initially evaluated 0.01 mol% under the same conditions gave 95% and 51% GC
using the Sonogashira cross-coupling reaction between yields, respectively (entries 2 and 3). This effect was further
iodobenzene and phenylacetylene. As shown in Table 1, when investigated by the kinetic curve of conversion versus palla-
dium loading (Fig. S1†). The variation of palladium loading
from 1 to 0.05 mol% has no significant effect on catalytic
activity of the reaction system, while a sharp decrement was
observed when palladium loading was below 0.05 mol%. The
effects of palladium sources and bases on the cross-coupling
reaction were also examined. PdCl2, Pd(cod)Cl2 and Pd(OAc)2
have been employed successfully as palladium sources, but
lower GC yields were obtained (entries 4–6). Among the bases
tested, NEt3 was found to be the most efficient (entry 2), and
Fig. 1 The charge distributions of dpa and Pd–dpa.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
other organic bases, such as (i-Pr)2NH and (n-Bu)3N, gave rise 68% GC yields under the same conditions, respectively, which
to 1,2-diphenylethyne in 26 and 30% GC yields, respectively are less efficient than dpa; however, the use of impy and pzpy
(entries 7 and 8). Inorganic bases, such as NaOAc, KOH, K3PO4 resulted in even lower GC yields, suggesting that dpa is a good
and Cs2CO3, were inefficient for the catalysis (entries 9–12). It promoter in the palladium-catalyzed Sonogashira cross-
should be mentioned that aqueous Bu4NOH was widely used coupling reaction in neat water.
as a base and a reaction medium in catalysis,12a but no desir-
To further explore the catalytic efficiency of this system, a
able product was detected when the coupling reaction was run more versatile and practical method was applied to cross-coup-
using 55% aqueous Bu4NOH as a base under identical con- ling reactions between aryl iodides and terminal alkynes by
ditions (entry 13). These results revealed a significant depen- using 0.1 mol% Pd(NH3)2Cl2–dpa as a precatalyst in the pres-
dence of the cross-coupling reaction on the nature of the ence of NEt3 in neat water at 25 °C for 6 h (Table 2). The effect
bases. Similar situations were also observed in the reported of varying aryl iodides in the reaction was initially tested by
Sonogashira cross-coupling reaction.6,7 It was recently pro- using phenylacetylene as a substrate, aryl iodides bearing elec-
posed that catalytic reactions in neat water occurred in the tron-withdrawing and electron-donating groups, such as
organic layer, while the water phase may dissolve polar reac- –Cl, –CF3, –F, –Me and –OMe, smoothly coupled with
tants and re-absorb side products.9d Because iodobenzene,
phenylacetylene and NEt3 are liquid, the Sonogashira cross-
Table 2 The Sonogashira cross-coupling reaction of aryl iodides with
terminal alkynesa
coupling reaction between iodobenzene and phenylacetylene
was performed in the absence of water, and a 72% GC yield
was obtained (entry 14).
As a comparison, other bidentate nitrogen-containing che-
lating ligands were also used as supporting ligands of palla-
dium in the reaction of iodobenzene and phenylacetylene
(Scheme 2). As shown in Fig. 3, 2,2′-bipy and phen gave 80 and
Entry
R1
R2
Yieldb (%)
1
2
3
4
H
4-Cl
4-CF3
4-F
H
H
H
H
95 (91)
91 (86)
91 (83)
83
5
6
7
8
4-Me
3-Me
2-Me
3,5-Dimethyl
4-H
4-Cl
4-CF3
4-F
4-Me
3-Me
2-Me
H
4-Cl
4-CF3
4-F
H
H
H
H
81
86 (82)
90 (86)
73
94 (89)
94 (83)
98 (95)
77
76
78
85 (72)
96 (91)
95 (86)
93 (90)
81
83
84
86 (77)
94 (87)
95 (89)
95 (90)
80
9
4-MeO
4-MeO
4-MeO
4-MeO
4-MeO
4-MeO
4-MeO
4-Me
4-Me
4-Me
4-Me
4-Me
4-Me
4-Me
3-Me
3-Me
3-Me
3-Me
3-Me
3-Me
2-Me
2-Me
2-Me
2-Me
2-Me
2-Me
4-MeCO
4-MeCO
4-MeCO
4-MeCO
4-MeCO
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
Scheme 2 The bidentate nitrogen-containing ligands used in this
work.
4-Me
3-Me
2-Me
H
4-Cl
4-CF3
4-Me
3-Me
2-Me
H
82
84
100 (91)
100 (95)
100 (92)
93 (87)
98 (90)
94 (83)
67
73
59
61
64
4-Cl
4-CF3
4-Me
3-Me
2-Me
H
4-CF3
4-Me
3-Me
2-Me
Fig. 3 The conversion of iodobenzene in the reaction of iodobenzene
and phenylacetylene using different nitrogen-containing ligands as sup-
porting ligands. Reaction conditions: iodobenzene (0.50 mmol), phenyl-
acetylene (0.75 mmol), Pd(NH3)2Cl2-ligand (0.1 mol%), Et3N (1.50 mmol),
and H2O (2.0 mL) at 25 °C for 6 h under N2.
a Reaction conditions: aryl iodide (0.5 mmol), alkyne (0.75 mmol), Pd-
(NH3)2Cl2–dpa (0.1 mol%), Et3N (1.50 mmol), and H2O (2.0 mL) under
N2 at 25 °C for 6 h. b GC yield; the isolated yield is given in
parentheses.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

View Article Online
Paper
Dalton Transactions
phenylacetylene (entries 2–7), and the corresponding products presence of NEt3. As shown in Table 3, when one drop of Hg(0)
were obtained in good to excellent yields, in which 4-chloro- was added to the reaction mixture before the reaction was
iodobenzene and 4-trifluoromethyl-iodobenzene gave slightly carried out, 1,2-diphenylethyne was formed in a 10% GC yield
higher GC yields than 4-fluoro-iodobenzene (entries 2–4). (entry 1), which is much lower than that under normal con-
Unexpectedly, the use of 2-methyl-iodobenzene also resulted ditions, and indicates the formation of Pd(0) active species
in a 90% GC yield (entry 7), which is higher than 4-methyl- and subsequent interaction with mercury to form amalgama-
iodobenzene (81%), 3-methyl-iodobenzene (86%) and 4-fluoro- tion, resulting in Pd(0) poisoning and low catalytic activity. On
iodobenzene (83%) regardless of their steric and electronic the other hand, pyridine and polyvinylpyridine (PVPy) are well
characteristics (entries 4–6). It is noteworthy that the reaction known for their good binding ability to palladium, but the
of 3,5-dimethyl-iodobenzene with phenylacetylene gave rise to insolubility of PVPy in water enables the palladium particles to
the target product in a 73% GC yield (entry 8). Interestingly, a be removed from water, resulting in an ineffective contact
similar conversion trend was observed for the alkynes bearing between catalysts and substrates as well as the extinguishment
–OMe (entries 9–15) and different steric hindrance (entries of catalytically active species. As expected, when 100 equivalent
16–34), in which ortho-, meta- and para-methyl substituents in amount of PVPy was used as an additive in the cross-coupling
the aromatic ring of the alkynes have no obvious effect on the reaction, no catalytic activity was observed (entry 2). However,
cross-coupling reactions; the resulting products were afforded the addition of 100 and 1000 equivalent amount of pyridine
in 76–100% GC yields. However, the electron-deficient 4-acetyl- resulted in 93 and 92% GC yields (entries 3 and 4), respect-
phenylacetylene provided the corresponding products in lower ively, which are close to those under normal conditions
GC yields (59–73%) than electron-rich 4-methyl-phenyl- (Table 2, entry 1).
acetylene and 4-methoxyl-phenylacetylene (entries 35–39). It is
The kinetic study further showed that the presence of pyri-
noteworthy that cross-coupling reactions of ortho-, meta- and dine resulted in a longer induction period and lower reaction
para-methyl substituted iodobenzene with phenylacetylene activity than that under normal conditions (Fig. 4). It should
gave the desired products in 81, 86 and 90% GC yields, be mentioned that the addition of 1000 equivalent amount of
respectively (entries 5–7); however, the same products were thiophene gave a 68% GC yield (entry 5), while no catalytic
obtained in 96, 94 and 100% GC yields in the reactions of activity was detected when 100 equivalent amount of PPh3 was
iodobenzene with ortho-, meta- and para-methyl substituted added to the reaction mixture. It should be mentioned that a
phenylacetylene under identical conditions (entries 16, 23 decrease of conversion from 95 to 68% was observed when the
and 29).
molar ratio of dpa to palladium was increased from 1 to 11
It was reported that palladium nanoparticles (NPs) may be (Table 3, entry 6), suggesting that excess of dpa was co-
formed after the cross-coupling reactions catalyzed by palla- ordinated around palladium NPs, inhibiting enough contact of
dium coordination complexes.17 The process is involved in the substrates with catalytically active sites.
reduction of palladium complexes and subsequent stabili-
In order to find more evidence of the formation of palla-
zation by the supporting ligands, and the resulting NPs usually dium NPs, after the Sonogashira cross-coupling reaction of
possess small size and narrow size distribution. To identify iodobenzene and phenylacetylene under normal conditions
palladium active species from the catalytic system, the mercury was finished, the crude mixture was extracted several times
drop test and poisoning experiments were performed in the
cross-coupling reaction of iodobenzene and phenylacetylene
using 0.1 mol% Pd(NH3)2Cl2–dpa as a precatalyst in the
Table 3 Summary of the poisoning experimentsa
Ratio of the additive
to palladium
Entry
Additive
Yieldb (%)
1c
2
3
4
5
6
7
Hg
PVPy
Pyridine
Pyridine
Thiophene
PPh3
—
10
0
93
92
68
0
100
100
1000
1000
100
11
Dpa
65
Fig. 4 The conversion of iodobenzene as a function of time for the
Sonogashira cross-coupling reaction of iodobenzene and phenyl-
acetylene in neat water at 25 °C: (a) under normal conditions; (b) after
100 equivalent amount of pyridine was added; (c) after 100 equivalent
amount of PVPy was added.
a Reaction conditions: iodobenzene (0.50 mmol), phenylacetylene
(0.75 mmol), Pd(NH3)2Cl2–dpa (0.1 mol%), Et3N (1.50 mmol), and H2O
(2.0 mL) at 25 °C for 6 h under N2. b GC yield. c One drop of Hg was
added.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
100 MHz, respectively, by using CDCl3 as a locking solvent
except where otherwise indicated. Chemical shifts were
1
reported in ppm relative to TMS for H and 13C NMR spectra.
Gas chromatography (GC) analyses were performed on a Shi-
madzu GC-2014 equipped with a capillary column (RTX-5,
30 m × 0.25 mm) using a flame ionization detector. Trans-
mission electron microscopy (TEM) was performed on a JEOL
JEM-2010 microscope and was operated at 200 kV.
Theoretical study
Calculations were carried out using the Gaussian 03 (Revision
Fig. 5 TEM images of palladium NPs after the Sonogashira cross- D.02) suite of programs.21 The geometric optimization of the
coupling reaction under normal conditions.
structures and frequency analyses were carried out using the
B3-LYP method with effective core potentials (ECPs). The all-
electron 6-31+G** basis set was used on C, N, Cl and H atoms
with ethyl ether, to the aqueous layer containing catalytically
while Lanl2dz developed by Hay and Wadt was employed to
active species was added ethanol and then centrifuged, and
describe the palladium atom.19 The vibration frequencies were
the suspended solid was directly placed as a thin film in a
used to characterize the optimized structures where the energy
carbon coated copper grid for TEM analysis. The TEM images
is minimal without imaginary frequencies on the potential
clearly showed the formation of palladium NPs with a mean
energy surface. The scaling factors are neglected in the harmo-
diameter of 2.3 nm and a standard deviation of 0.5 (Fig. 5).
nic vibration frequencies.
General procedures for preparation of a stock solution
of Pd–dpa. The commercially available palladium(II)
(0.025 mmol) and 2,2′-dipyridylamine (4.3 mg, 0.025 mmol)
The size is smaller than those of the reported palladium NPs
in situ generated after the cross-coupling reaction in water,18
which is probably ascribed to the low reaction temperature in
the catalytic system. Interestingly, the palladium NPs are
were added into distilled water (5.0 mL), and the resulting
stable in aqueous solution, and no precipitate was observed
mixture was oscillated until a yellow solution was formed,
for weeks.
which was used as a stock solution for catalysis. The concen-
tration of the stock solution is CPd = 0.005 mol L−1
.
General procedures for the palladium-catalyzed Sonogashira
cross-coupling reaction. A mixture of the aryl iodide
(0.50 mmol), aromatic alkyne (0.75 mmol) and base
(1.50 mmol) and an appropriate amount of a stock solution of
Pd–dpa in H2O (2 mL) was stirred under N2 at 25 °C. After 6 h,
the resulting mixture was extracted with ethyl acetate (3 ×
5 mL), the combined organic layer was dried over anhydrous
MgSO4 and the solvent was removed under reduced pressure.
The crude products were purified by flash column chromato-
graphy on silica gel to afford the desired products. The identity
of the products was confirmed by comparison with literature
spectroscopic data.
Conclusion
We have developed a non-phosphorus catalytic system for the
Sonogashira cross-coupling reaction of aryl iodides with term-
inal alkynes in neat water at room temperature. The reaction
was promoted by 2,2′-dipyridylamine in the absence of copper.
Interestingly, both 2,2′-dipyridylamine and commercially avail-
able palladium sources are insoluble in neat water, but their
mixture can dissolve in water, resulting in superior catalytic
performances in the Sonogashira cross-coupling reaction at
room temperature. The kinetic study, the mercury drop test,
poisoning experiments and TEM analysis revealed that palla-
dium nanoparticles with small size and narrow size distri-
bution were formed after the catalytic reaction. This study has
extended the scope of the Sonogashira cross-coupling reaction
in water, and provided an environmentally benign route for
the synthesis of temperature-sensitive 1,2-disubstituted alkyne
compounds. Further investigation to broaden the scope of the
catalytic system to other reactions is in progress.
Acknowledgements
This work was financially supported by the 973 Program
(2010CB933501 and 2011CBA00502), the Natural Science Foun-
dation of China (21273239), the Natural Science Foundation of
Fujian Province (2011J01064) and the “One Hundred Talent
Project” from the Chinese Academy of Sciences.
Experimental section
General
Notes and references
The impy19 and pzpy20 were synthesized according to literature
methods. The other chemicals were obtained from commercial
suppliers and used without further purification. 1H and 13C
NMR spectra were recorded on spectrometers at 400 and
1 (a) J. Dupont, R. F. de Souza and P. A. Z. Suarez, Chem.
Rev., 2002, 102, 3667–3692; (b) J. M. Liu, X. G. Peng,
W. Sun, Y. W. Zhao and C. G. Xia, Org. Lett., 2008, 10,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

View Article Online
Paper
Dalton Transactions
3933–3936; (c) D. M. Cartney and P. J. Guiry, Chem. Soc. 10 (a) K. H. Shaughnessy, Chem. Rev., 2009, 109, 643–710;
Rev., 2011, 40, 5122–5150; (d) F. A. Harraz, S. E. El-Hout,
H. M. Killa and I. A. Ibrahim, J. Catal., 2012, 286, 184–192;
(e) G. V. Johannes, Dalton Trans., 2006, 421–429.
2 (a) R. Chinchilla and C. Nájera, Chem. Soc. Rev., 2011, 40,
5084–5121; (b) R. Chinchilla and C. Nájera, Chem. Rev.,
2007, 107, 874–922; (c) H. Doucet and J. C. Hierso, Angew.
Chem., Int. Ed., 2007, 46, 834–871; (d) J. R. Harjani,
(b) D. J. M. Snelders, R. Kreiter, J. Firet, G. van Koten and
R. J. M. K. Gebbink, Adv. Synth. Catal., 2008, 350, 262–266.
11 (a) S. N. Chen, W. Y. Wu and F. Y. Tsai, Green Chem., 2009,
11, 269–274; (b) W. Y. Wu, S. N. Chen and F. Y. Tsai, Tetra-
hedron Lett., 2006, 47, 9267–9270; (c) M. Mifsud,
K. V. Parkhomenko, I. W. C. E. Arends and R. A. Sheldon,
Tetrahedron, 2010, 66, 1040–1044.
T. J. Abraham, A. T. Gomez, M. T. Garcia, R. D. Singer and 12 (a) C. S. Zhou, J. Y. Wang, L. Y. Li, R. H. Wang and
P. J. Scammells, Green Chem., 2010, 12, 650–655;
(e) N. M. Jenny, M. Mayor and T. R. Eaton, Eur. J. Org.
Chem., 2011, 4965–4983.
M. C. Hong, Green Chem., 2011, 13, 2100–2106;
(b) F. Z. Kong, C. S. Zhou, J. Y. Wang, Z. Y. Yu and
R. H. Wang, ChemPlusChem, 2013, 78, 536–545.
3 (a) E. Christiansen, M. E. Due-Hansen and T. Ulven, J. Org. 13 (a) L. Y. Li, J. Y. Wang, C. S. Zhou, R. H. Wang and
Chem., 2010, 75, 1301–1304; (b) A. Scarpaci,
A. Nantalaksakul, J. M. Hales, J. D. Matichak, S. Barlow,
M. Rumi, J. W. Perry and S. R. Marder, Chem. Mater., 2012,
24, 1606–1618.
M. C. Hong, Green Chem., 2011, 13, 2071–2077; (b) L. Y. Li,
J. Y. Wang, T. Wu and R. H. Wang, Chem.–Eur. J., 2012, 18,
7842–7851; (c) D. Zhang, C. S. Zhou and R. H. Wang, Catal.
Commun., 2012, 22, 83–88.
4 (a) H. Huang, H. Liu, H. L. Jiang and K. X. Chen, J. Org. 14 (a) M. R. Buchmeiser and K. Wurst, J. Am. Chem. Soc., 1999,
Chem., 2008, 73, 6037–6040; (b) O. Vechorkin, D. Barmaz,
V. Proust and X. L. Hu, J. Am. Chem. Soc., 2009, 131, 12078–
12079; (c) J. Alex, M. S. Mobin and G. Prasenjit, Dalton
Trans., 2009, 10581–10591.
5 (a) H. B. Li, C. C. C. J. Seechurn and T. J. Colacot, ACS
Catal., 2012, 2, 1147–1164; (b) D. H. Lee, Y. H. Lee,
J. M. Harrowfield, I. M. Lee, H. I. Lee, W. T. Lim, Y. Kim
and M. J. Jin, Tetrahedron, 2009, 65, 1630–1634.
121, 11101–11107; (b) J. Silberg, T. Schareina, R. Kempe,
K. Wurst and M. R. Buchmeiser, J. Organomet. Chem., 2001,
622, 6–18; (c) B. Karimi, S. Abedi, J. H. Clark and
V. Budarin, Angew. Chem., Int. Ed., 2006, 45, 4776–4779;
(d) Y. Hu, Y. Y. Yu, Z. S. Hou, H. Li, X. G. Zhao and
B. Fenga, Adv. Synth. Catal., 2008, 350, 2077–2085;
(e) Y. Uozumi and Y. M. A. Yamada, Chem. Rec., 2009, 9,
51–65.
6 (a) Y. T. Chu, K. Chanda, P. H. Lin and M. H. Huang, Lang- 15 (a) M. J. Rauterkus, S. Fakih, C. Mock, I. Puscasu and
muir, 2012, 28, 11258–11264; (b) T. Suzuka, Y. Okada,
K. Ooshiro and Y. Uozumi, Tetrahedron, 2010, 66, 1064–
1068; (c) A. N. Marziale, J. Schlüter and J. Eppinger, Tetrahe-
B. Krebs, Inorg. Chim. Acta, 2003, 350, 355–365;
(b) M. D. Zvikovic, S. Rajkovic, U. Rychlewska, B. Warzajtis
and M. I. Djuran, Polyhedron, 2007, 26, 1541–1549.
dron Lett., 2011, 52, 6355–6358; (d) T. Teratani, A. Ohtaka, 16 Gaussian 03 (Revision D.02), Gaussian, Inc., Wallingford,
T. Kawashima, O. Shimomura and R. Nomura, Synlett, CT, 2004.
2010, 2271–2274; (e) B. H. Lipshutz, D. W. Chung and 17 (a) K. Yu, W. Sommer, J. M. Richardson, M. Weck and
B. Rich, Org. Lett., 2008, 10, 3793–3796.
C. W. Jones, Adv. Synth. Catal., 2005, 347, 161–171;
(b) D. A. Alonso and C. Nájera, Chem. Soc. Rev., 2010, 39,
2891–2902; (c) B. Karimi and P. F. Akhavan, Inorg. Chem.,
2011, 50, 6063–6072; (d) D. B. Zhao, Z. F. Fei,
T. J. Geldbach, R. Scopelliti and P. J. Dyson, J. Am. Chem.
Soc., 2004, 126, 15876–15882.
7 (a) J. Gil-Moltó and C. Nájera, Eur. J. Org. Chem., 2005,
4073–4081; (b) J. Gil-Moltó, S. Karlström and C. Nájera,
Tetrahedron, 2005, 61, 12168–12176; (c) B. Liang, M. L. Dai,
J. H. Chen and Z. Yang, J. Org. Chem., 2005, 70, 391–393;
(d) J. Gil-Moltóa and C. Nájeraa, Adv. Synth. Catal., 2006,
348, 1874–1882; (e) M. Z. Cai, Q. H. Xu and J. C. Sha, J. Mol. 18 (a) I. B. Inés, R. SanMartin, M. J. Moure and E. Domínguez,
Catal. A: Chem., 2007, 272, 293–297.
8 J. G. Concepciόn, A. D. Curzons, D. J. C. Constable and
V. L. Cunningham, Int. J. Life Cycle Assess., 2004, 9, 114–
121.
Adv. Synth. Catal., 2009, 351, 2124–2132; (b) S. Sawoo,
D. Srimani, P. Dutta, R. Lahiri and A. Sarkar, Tetrahedron,
2009, 65, 4367–4374; (c) D. Saha, K. Chattopadhyay and
B. C. Ranu, Tetrahedron Lett., 2009, 50, 1003–1006.
9 (a) C. J. Li, Chem. Rev., 2005, 105, 3095–3165; 19 R. H. Wang, J. C. Xiao, B. Twamley and J. M. Shreeve, Org.
(b) M. Lamblin, L. Nassar-Hardy, J. C. Hierso, E. Fouquet Biomol. Chem., 2007, 5, 671–678.
and F. X. Felpin, Adv. Synth. Catal., 2010, 352, 33–79; 20 A. J. Amoroso, A. M. C. Thompson, J. C. Jeffery, P. L. Jones,
(c) V. Böhrsch and C. P. R. Hackenberger, ChemCatChem.,
2010, 2, 243–245; (d) C. Röhlich, A. S. Wirth and K. Köhler,
Chem.–Eur. J., 2012, 18, 15485–15494.
J. A. McCleverty and M. D. Ward, J. Chem. Soc., Chem.
Commun., 1994, 2751–2752.
21 P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299–310.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014